Process for production of composite bulk yarn

ABSTRACT

The present invention is an improvement in the method of producing a composite bulk yarn of a false-twist type. Composite bulk yarns produced by the conventional false-twisting methods have inconsistent shapes and a poor hand and some yarns are of little value commercially. However, it is found that with an appropriate process condition, a grouping of composite bulk yarns having an excellent hand can be provided. In the present invention, the grouping has been standardized and an attempt has been made to find a process for the production of the standardized composite bulk yarn. Two empirical formulas are offered with respect to the steps of selecting the process conditions. With the use of the two empirical formulas, it becomes easy to frame a plan to produce the standardized composite bulk yarn. This invention has also attained means of always securing high quality products more pleasing to the touch.

United States Patent [191 Sasaki et al.

[111 3,844,103 [451 Oct. 29, 1974 PROCESS FOR PRODUCTION OF COMPOSITE BULK YARN Inventors: Yoshiyuki Sasaki, Takatsuki;

Masayuki Tani, Ibaragi, both of Japan Assignee: Teijin Limited, Osaka, Japan Filed: May 29, 1973 Appl. No.: 364,421

US. Cl 57/157 TS, 57/144, 57/160 Int. Cl D02g 1/02, D02g 3/36 Field of Search 57/34 HS, 157 TS, 34 AT,

References Cited UNITED STATES PATENTS Primary Examiner--John Petrakes Attorney, Agent, or Firm-Sherman & Shalloway [5 7 ABSTRACT The present invention is an improvement in the method of producing a composite bulk yarn of a falsetwist type. Composite bulk yarns produced by the conventional false-twisting methods have inconsistent shapes and a poor hand and some yarns are of little value commercially. However, it is found that with an appropriate process condition, a grouping of composite bulk yarns having an excellent hand can be provided. In the present invention, the grouping has been standardized and an attempt has been made to find a process for the production of the standardized composite bulk yarn. Two empirical formulas are offered with respect to the steps of selecting the process conditions. With the use of the two empirical formulas, it becomes easy to frame a plan to produce the standardized composite bulk yarn. This invention has also attained means of always securing high quality products more pleasing to the touch.

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sum "12 or 12- PROCESS FOR PRODUCTION OF COMPOSITE BULK YARN The present invention relates to improvements in a false-twist process for the production of a twist-like composite bulk yarn. Thermoplastic filament yarns have no bulkness but rather have an undesirable hand and are smooth without further processing. Attempts have been made to eliminate the defect and produce what is called a processed yarn having a wool-like hand or spun yarn appearance. For instance, the filaments are looped or curled to increase the bulkness or the orientation of filaments parallel to one another along the length of the filament yarn is disturbed by a hard twist to cause the filaments to run inclinedly relative to the yarn axis. Or with the use of size, a core yarn is covered with bulk yarn. Each finished yarn described above has a quality defect and satisfactory results have not yet been obtained.

The inventors have found improvements in Japanese Patent Publication No. 28018/70, in which around filaments which are being false twisted as a core, a sheath yarn is wrapped as a covering yarn and both the yarns are heat set into a composite bulk yarn. While the invention of the above patent publication was being practised, various types of research were conducted to find improvements in methods of producing the yarns. The present invention relates to those improvements, which are described below.

When the above-described prior art was put into practice, it was found that according to various factors such as denier, number of false twists and the percentage of overfeed of a sheath yarn, the shapes and appearances of the composite bulk yarns thus produced are varied to a great extent. In other words,.the composite yarns differ greatly from each other in quality. In the present invention, composite yarns having the desired appearance have been selected and the selected yarns are standardized. It is the object of the present invention to produce this standardized yarn.

As described above, denier, the number of falsetwists and the percentage of overfeed of a sheath yarn are the factors in producing a composite bulk yarn. The selection of the three factors becomes a problem. If the selection is improper, the production of the standard composite bulk yarn will fail. Some guides for the selection are required and in the present invention they are found empirically rather than theoretically.

Let the denier sizes of a core yarn A and a sheath yam B be expressed as D, and D Since it is compli cated to handle them separately for simplicity the denier size of the yamsis represented by D D Then, let Tn (turn per meter) stand for the number of false twists of the core yarn A. Let the relationship between Tn and D, D be considered. It should be noted that the number of false twists Tn of the core yarn has to have given limitations for a given core yarn. For instance, if the Tn is too great, the yarn tends to break during the processing and a production obstacle is caused. Conversely, if it is too small, the wrapping angle becomes obtuse and ample wrapping'is not ob tained. Accordingly, it is understood that the production of a standard compositebulk yarn with a certain size, D, D is limited to a given range of Tn and the composite bulk yarn will fail to stand a test beyond the limitations. Experimentation has been carried out with the use of various denier sizes of D, D to determine the relationship between D A D and Tn.

11 BB B 1 For instance, when D, D is given, Tn is calculated by the formula l The Tn suitable for a standard composite bulk yarn lies within the range of Tn obtained by substituting [5,, I5 for the formula l The desired Tn ranges from the lower limit K 2.4 to the upper limit K 4.2. ,The desired Tn lies within the range of the upper and lower limits.

Let the running length of a core yarn A be I, and the extended length of a wrapped yarn B be 1 in a unit time. The overfeed of the wrapped yarn is calculated by the following formula:

Overfeed percent R =1 1 /1,

Besides D, D and Tn, R will be one of the important factors for producing the standard composite bulk yarn. Even if an appropriate value of Tn is selected in the formula l a standard composite bulk yarn is not always obtained. It is essential to admit R as an important factor and give an appropriate value to R.

In principle, R should be related to D, D and Tn, but forming an empirical formula with the use of three variables becomes exceedingly difficult and complicated. Thus the relation between k in the formula l) and R is considered. This k has relation to Tn and D, D also. Empirically, the following formula (2) is obtained:

(2) In like manner, R has a range of appropriate values as Tndoes.

The formulas l) and (2) are utilized as follows: After the optional selection of D, D the propriety of Tn will be determined by the formula l At this time, the value of k is also determined. Substituting this k for the formula 2), one may determine the upper and lower limits of R and choose whatever overfeed percent R is appropriate. However, in order to obtain the best composite bulk yarn, it is necessary to rechoose appropriate values of Tn and R several times.

As described before, under a normal operating condition with D A D Tn and R selected properly, a standard composite bulk yarn is supposed to be obtained. However, if a malfunction occurs during the operation, the wrapping condition is varied rapidly and a standard hand is damaged. For instance, when yarn is drawn off the bobbin inconsistently, R is varied and with changes in revolution of a twist spindle, Tn is changed suddenly. In the present invention, such obstacles can be prevented from affecting the wrapping directly.

The composite bulk yarn described above is greatly improved in its appearance by a napping process. The improved appearance is not obtained until the standard composite bulk yarn obtained in the present invention is given a napping finish. Still further, two or more differently colored yarns may be combined into one sheath yarn to make a much more conspicuous appearance of the composite bulk yarn. Such differently colored appearance can only be obtained with the use of the composite bulk yarn of the present invention.

ln-order that the invention may be more clearly understood and readily carried into effect, one embodiment thereof will now be described, with reference to the accompanying drawings in which:

FIG. 1 shows a schematic representation of an apparatus which has been adapted for use in producing the composite bulk yarn of the present invention;

FIG. 2 is a side view showing various kinds of composite bulk yarns to be produced by the process of the present invention;

FIG. 3 is a side view showing such a state that a sheath yarn begins to wrap itself around a core yarn;

FIG. 4 is a diagrammatic view showing fundamental data for preparing the formula 1);

FIGS. 5, 6, 7 and 8 are diagrammatic views showing fundamental data for preparing the formula (2);

FIG. 9 is a diagrammatic view showing the cohesive state of the core and sheath yarns in a composite bulk yarn in the present invention;

FIG. 10 is a diagram showing the relation among Q, R and Tn;

FIGS. 11, 12 and 13 show other cohesive states of the core and sheath yarns in a composite bulk yarn in the present invention, respectively;

FIG. 14 is a diagram showing an apparatus for producing a napped composite bulk yarn;

FIG. 14 is a schematic view showing a contact angle made by a revolving napper machine and a composite bulk yarn;

FIG. 15 is a diagram for napping;

FIG. 16 is a diagram showing an apparatus for combining two or more standard composite bulk yarns and giving them a napping process;

FIG. 17 is a diagram showing two differently colored sheath yarns to be wrapped around a core yarn.

In FIG. 1, a core yarn A is fed to a take-up bobbin 7 through feed rollers l, a heater 2, a twist spindle 4 and delivery rollers 5,during which time the core yarn A is false twisted with the twist spindle 4. The false twist extends to the core yarn A ahead of the heater 2. A sheath yarn B joins thecore yarn A to be false twisted through feed rollers 3 ahead of the heater 2 and is caused to wrap itself around the core yarn A with the revolution of the core yarn-A. Both yarns turn into a composite bulk yam C and run. The composite yarn C is heat set to some extent when passing through the heater 2, and is not completely detwisted after leaving the twist spindle 4, keeping an alternately twisted state. The sheath yarn B stays around the core yarn A in a cohesive state and both yarns are integrated to form a type of bulk yarn. The shapes, and appearances of the bulk yarn are not uniform and are varied, because they are affected by D,, D Tn and R.

In the presentinvention, the composite bulk yarns thus produced are divided into two types, a standard yarn and a reject, which are illustrated in FIG. 2. In this example, only R is varied with D,, D and Tn set as constant. The results are shown in composite bulk yarns (D), (E), (F) and (G). In the case of D, R is about 0.1 and wrapping is insufficient. Though it is bulked, it is a reject which fails test. In the case of E, R is about 0.5 and wrapping is alternate and uniform. In the case of F, R is about 1.0 and alternate wrappings are exceedingly increased in number. E and F are standard composite bulk yarns. In the case of G, R is about 2.2 and the appearance is not a twist-like one but takes a loop form. This is a reject which fails test. Such are examples in which only R has been varied, but it is empirically found that the cases when only Tn or only D, D B is varied are analogous.

The standard composite yarn in the present invention has, in general, alternate wrappings as shown in the composite yarns E and F. The feature of the present invention is how to produce such a standard composite bulk yarn and more particularly how to select appropriate values of various factors such as D D,,, Tn and R participating in the manufacture of the standard composite yarn with the use of an apparatus of FIG. I. The selection of the factors is essential and the empirical formulas 1) and (2) are provided to be a guide for the selection. The formation of the formulas will be described below.

In FIG. I, the core yarn A and the sheath yarn B are joined to each other at a point P and the sheath yarn B wraps itself around the core yarn A to make the yarn C as shown in FIG. 3. The sheath yarn B is spirally wrapped around the periphery of the core yarn A and its wrapping density, the number of wrappings, etc. vary with changes in the above-described factors. The composite yarn C is heat set with the heater 2. When the yarn C passes through the twist spindle 4, the twist direction of the yarn C is reversed such that detwist operations are carried out. Here the yarn C is subjected to remarkable changes in the shape. The course of changes will be described referring to FIG. 2. In the case of D, the yarn is much detwisted. When R is increased, the yarn shows an alternate twist-like condition as in E and F. The'sheath yarn D does not separate from the core yarn A and they are in a cohesive state. When R becomes greater, the yarn takes the shape in which the appearance becomes unsatisfactory. The present invention has standardized a composite yarn and maintained it in the range of E and F, which means that the standard yarn has tolerances and the values of the factors are to be selected from a certain range.

The formation of the following empirical formula will be described below. a

Tn M ',/.D,, D D,, D With the use of an apparatus as shown in FIG. 1, experiments on the manufacture of composite yarns were carried out. The test results are shown in FIG. 4. In the experiment, 11 specimens having a range of 60 to 500 denier sizes of D,, D were used. They are plotted as abscissa. Tn ranging from 1,000 to 6,000 turns per meter is plotted as ordinate with an interval of 500 turns per meter. The marks 0 show that all the composite yarn specimens stay within the range of standard types and are reported as passes test and the marks X denote rejects which fails test. In the experiments, an appropriate R was used. The marks 0 near the marks X are connected with each other to obtain the curves of upper and lower limits. If Tn within a zone enclosed with the upper and lower limit curves is used, a standard composite bulk yarn is obtained and if Tn is taken outside the zone, it will make an objectionable composite yarn. Both curves have a similar trend to each other and Tn can beexpressed as:

in the case of the lower limit, the constant k is 2.4. In short,

is obtained.

In using the formula( I), first, D A D is selected and substituted for the formula l) to calculate Tn, which has a scope in which the constant k ranges from 2.4 to 4.2.

The formation of the formula 2) will, then, be described below.

Overfeed percent R of a sheath yarn is empirically acknowledged as being one of the important factors in manufacturing a composite bulk yarn, but it is extremely difficult to place R in the formula. Consideration has been given to various steps to solve the problem. As a result, the following idea has been arrived at: The constant k of the formula 1) can be related to R. First, let D A D, have a given denier size, and the relation between Tn and R is tested on the yarn having a given denier size. In this case Tn can be converted to the constant k of the formula l Hence, the relation of the converted k and R can be determined. One embodiment is shown in FIG. 5. In FIG. 5, the denier size of a composite yarn is 100 denier. With the use of the 100 denier specimen, Tn is converted into k and the k is plotted as abscissa and B as ordinate. The marks show passes test standard yarns and the marks X fails test. Thus, the upper and lower limit curves enclose a range of passes test. As shown in FIGS. 6 and 7, experiments with 200 and 300 denier yarns are analogous. In comparison among FIGS. 5, 6 and 7, it should be noted that the upper limit curves and the lower limit curves have a trend similar to each other. Let the marks, passes test and fails test of the diagrams be redrawn on one of the diagrams and FIG. 8 is obtained. As shown in FIG. 8, the curves overlap with each other. It is also found that other specimens having a denier size other than those in the experiments are analogous.

In FIG. 8, the lower limit curve gives an empirical formula R 0.3/7 (k 1.2) and the upper limit curve an empirical formula R 07/6 (k 1.2) 0.1, which makes the formula 2) It should be understood that irrespective of DA+ D the relation as shown in the formula (2) exists weenkandL... a--- lnsummary, in producing the standard composite bulk yarn of the present invention, D A D will first be determined; it is substituted for the formula l) to find the scope of Tn. An appropriate turn of false twist may be selected from this scope. The k corresponding to it is found and substituted for the formula 2) to obtain the scope of R. The desired. R is selected from within this scope.

As described before, Tn and R have a certain range and it seems that the standard composite yarn can produce an appearance having a certain range. Whatever appearance is desired may be chosen from the range. Thus, a correct course for manufacturing a standard composite bulk yarn can be taken.

Even when various factors such as D A D Tn and R satisfy the requirements in carrying out the operation, and a standard composite bulk yarn is supposed to be produced, a composite yarn is subjected to slubs or tends to break easily at the twist-spindle when variations during the operations, for instance irregularities of Tn or R occur. Sudden changes in Tn, which are mainly due to the non-uniform drawing off of yarn, easily occur when the apparatus is restarted from machine downtime. The occurrence of such an obstacle prevents the manufacture of a standard composite bulk yarn. The inventors have successfully found the following counter-measure:

As shown in FIG. 9, the sheath yarn B joins the core yarn A under false twisting and wraps itself around the core yarn A to produce a composite bulk yarn C. The yarns proceed in the arrow direction and the yarns A, B and C are balanced by D D Tn and R. For instance, the A-P-B angle 0 is not constant and varies under the influence of the factors as the case may be. The test results are graphed in FIG. 10. R is plotted as abscissa and 0 as ordinate. With Tn and D, D kept constant, the relation between R and 6 is determined. When R is 0.4, Tn is 3,200 turns per meter and 6 takes 110. With the 0,, the yarns A, B and C are balanced. When Tn turns into 2,700 t/m, 6 becomes The changes in the balance are illustrated in FIGS. 9 and 11. In FIG. 9, R is 0.4, Tn is 3,200 t/m and 6 takes the yarns A, B and C are balanced at a point P. In FIG. 11, when with the same R of 0.4, Tn changes into 2,700 t/m, a new balance appears and the angle 8, becomes an angle 6, of 80. With such phenomena in mind, steps to eliminate the obstacle are taken:

In FIG. 12, the yarns are supposed to be balanced at a point P in the normal operating condition. If a thread guide M is provided to force the point P to move to P", the yarn B is urged against the thread guide M. If the thread guide M is removed, the yarn B will return to the point P rapidly. This force of restoration always presses the thread guide M, and the yarn B and the thread guide M are always in tight engagement with each other to secure the accurate supply of a sheath yarn. Uniform wrapping even at a very fine pitch is feasible.

What is more important, the provision of the thread guide M helps prevent defective processing. When the processing factors such as Tn and R have a sudden change, their influence can be alleviated with this thread guide. In FIG. 12, let any factor change suddenly. If there is no thread guide attached, the wrapping point will move from P and a different balanced state appears. Let the wrapping point at the time be P. During this movement, the composite condition will become irregular.

However, if in FIG. 12, the wrapping point is always kept as being transferred to a point P" with the thread guide M, a sudden change of the processing factors, if any, will not directly influence the wrapping. No transfer of the point P to the point P' occurs and force to cause the movement is interrupted with the thread guide M. The engagement condition of the yarn B with the thread guide M is naturally affected to some extent but the wrapping will be little affected. The same effect can be expected even when the processing factors cause the wrapping point P to transfer to a point P opposite to the point P.

In short, irregularities of a composite bulk yarn can be prevented by observing a transfer range of the wrapping point P to be caused by variations of the processing factors and positioning the thread guide M suffrciently apart from the transfer range of the point. Such is a-concomitant device for a process for the production of a standard composite bulk yarn.

Then, improvements in a standard composite bulk yarn will be described below.

In FIG. 2, E and F belong to the scope of a standard composite yarn and when a further napping process is given, a composite bulk yarn H having a high loftiness is obtained. One embodiment of the napping process is shown in FIG. 14. The composite bulk yarn C is passed in a tight condition over a revolving napper machine 8 having a rough surface midway between a heater 2 and a twist spindle 4 and part of the sheath yarn is broken. If the yarn passes through the twist spindle in this state, the yarn is subjected to detwisting and the napped filaments are partly mingled and wrapped. This state can be obtained by napping the standard composite bulk yarn, not the off-standard yarns D or G as shown in FIG. 2. In comparison of the conventional napping with the napping of the present invention, the former evidences that all orpart of the filaments constituting a yarn are broken and uniform napping cannot be obtained when the yarn is napped with a revolving napper machine 8. The conventional napping can be applied only to an exceedingly heavy denier yarn. In the present invention, it is a sheath yarn that is broken and napped, but the core yarn is not subjected to napping. Hence, the yarn can be processed uniformly and stably. Further, the standard composite bulk yarns E and F in FIG. 2 are most easily napped because the yarns are not over-wrapped or short wrapped. The yarns such as D and G other than E and F cannot be given naps with a good appearance. In the case of D, the core yarn is sometimes broken and in the case of G, wrapping becomes loosened, the revolving napper machine 8 catches the yarn increasingly and the yarn tends to break more.

In FIG. 14, when a composite bulk yarn comes in contact with the peripheral surface of a revolving napper machine 8 and a napping process is conducted, it is conceivable that the raised nap is controlled by the length of contact between the rough surface of the napper machine and the composite bulk yarn, and the degree of velocity difference between the two. The contact length may be considered proportional to an angle a as shown in FIG. 14. The velocity difference between the two can be expressed in WV where V denotes a revolving velocity of the revolving napper machine 8 and v the velocity of a composite yarn.

The experimental results are shown in FIG. 15. The angle or is plotted as abscissa and the velocity difference V/v as ordinate. The marks in the diagram show that the napping has a spun-yarn-looking appearance and the marks X shows that little nap was raised. The boundary between them is indicated by a dashed line. The test results indicate that an angle a is preferably arranged at 5 'to 30 and the formula 11, V/v 3 is appropriate in conjunction with V/v.

As described above, in the present invention, a composite bulk yarn having a lofty appearance can be produced by'napping. Further improvements will be obtained by a combination of the standard composite bulk yarns. A composite bulk yarn for use in heavy fabrics can well be produced with further processing by the process of the present invention. For example, at least two standard composite bulk yarns produced according to the present invention can be joined into one heavy denier yarn and this heavy denier yarn then napped. Alternatively at least two napped composite bulk yarns may be combined into one heavy denier yarn. The description with reference to FIG. 1 applies to a process for the production of a composite bulk yarn in FIG. 16 with the use of feed rollers l, a sheath yarn B, feed rollers 3, a heater 2 and a twist spindle 4. A process for the production of a composite yarn with a core yarn A and a sheath yarn B is analogous. Th composite yarns C and C thus produced are what are called standard composite bulk yarns in the present invention. The composite yarns C and C are laid together with a thread guide 10 and led to a revolving napper disc 8 driven separately from the yarn and passed inclinedly over the rough surface of the napper disc 8. In this case, the composite yarns C and C are subjected to napping and false twisting at the same time and incorporated into a cohesive state. Broken fibers are intermingled and thereby a highly lofty, bulk, heavy denier yarn is obtained. The angle B of the composite bulk yarn made by the yarn and the peripheral surface of the napper disc is preferably more than 30. In still another improvement, a yarn such as the yarn I in FIG. 2 is obtained. As shown in FIG. 17, a sheath yarn B is composed of two or more yarns having different colors. The subsequent processes for the production of the multi-colored composite bulk yarn are analogous. The sheath yarn B also may be a combination of a plurality of yarns having different dye affinities and capable of being dyed after the manufacture of a composite yarn or fabrics thereof.

What we claim is:

1. In a process for the production of a composite bulk yarn comprising heat setting a thermoplastic multifilament core yarn A and a thermoplastic multifrlament sheath yarn B while the sheath yarn B is being wrapped around the core yarn A under false twisting and detwisting and winding both yarns A and B without separating them, the improvement comprising using essential factors for the production of the composite bulk yarn by selecting proper values of Tn and R from the scope of the Tn and R calculated by the empirical formulas (2 wherein Tn denotes the number of false twist of the core yarn, D, the denier of the core yam'A, D the denier of the sheath yarn B, R the overfeed percent of the sheath yarn B, and K is a constant of 2.4 to 4.2, thus standardizing the composite bulk yarn having the sheath yarn B in alternate twist-like condition.

2. The process for the production of the standard composite yarn as set forth in claim 1 in which a thread guide is arranged along the core yarn to be engaged with the sheath yarn and sufficiently spaced apart from the normal wrapping point of the sheath yarn such that variations of processing factors during the operations do not adversely affect the wrapping condition.

3. The process for the production of the standard composite bulk yarn as set forth in claim 1 wherein part of the sheath yarn is napped after the heat-setting of the composite yarn by scratching up the sheath yarn with a napper machine and both the yarns are detwisted to intermingle the sheath yarn around the core yarn in an alternating twist-like condition.

4. A process for the production of a standard com posite bulk yarn comprising laying together at least two standard composite yarns produced by the process of claim 1, and napping them with a napper machine while they are being false twisted such'that broken fibers are intermingled with one another.

5. A process for the production of the standard composite bulk yarn as set forth in claim 1 in which two or more color yarns in combination are wrapped around the core yarn. 

1. In a process for the production of a composite bulk yarn comprising heat setting a thermoplastic multifilament core yarn A and a thermoplastic multifilament sheath yarn B while the sheath yarn B is being wrapped around the core yarn A under false twisting and detwisting and winding both yarns A and B without separating them, the improvement comprising using essential factors for the production of the composite bulk yarn by selecting proper values of Tn and R from the scope of the Tn and R calculated by the empirical formulas 2.4 X 104/ square root DA + DB < Tn < 4.2 X 104/ square root DA + DB (1) 0.3/7 (k 1.2)2 < R < 0.7/6 (k - 1.2)2 + 0.1 (2) wherein Tn denotes the number of false twist of the core yarn, DA the denier of the core yarn A, DB the denier of the sheath yarn B, R the overfeed percent of the sheath yarn B, and K is a constant of 2.4 to 4.2, thus standardizing the composite bulk yarn having the sheath yarn B in alternate twist-like condition.
 2. The process for the production of the standard composite yarn as set forth in claim 1 in which a thread guide is arranged along the core yarn to be engaged with the sheath yarn and sufficiently spaced apart from the normal wrapping point of the sheath yarn such that variations of processing factors during the operations do not adversely affect the wrapping condition.
 3. The process for the production of the standard composite bulk yarn as set forth in claim 1 wherein part of the sheath yarn is napped after the heat-setting of the composite yarn by scratching up the sheath yarn with a napper machine and both the yarns are detwisted to intermingle the sheath yarn around the core yarn in an alternating twist-like condition.
 4. A process for the production of a standard composite bulk yarn comprising laying together at least two standard composite yarns produced by the process of claim 1, and napping them with a napper machine while they are being false twisted such that broken fibers are intermingled with one another.
 5. A process for the production of the standard composite bulk yarn as set forth in claim 1 in which two or more color yarns in combination are wrapped around the core yarn. 